1. Field of the Invention
The present invention relates to a semiconductor device and a method for fabricating the same, and more particularly, to a semiconductor device and a method for fabricating the same, to completely fill a minute contact hole having a high aspect ratio with a refractory metal layer.
2. Discussion of the Related Art
In general, with high integration of a semiconductor device, a MOS (metal oxide semiconductor) transistor, one component of the semiconductor device, becomes minute. Thus, source and drain electrodes and a gate electrode, provided in the MOS transistor, decrease, and a metal line decreases. As the decrease of the metal line, it is necessary to decrease a contact hole between the gate electrode and the metal line, and between the source/drain electrodes and the metal line. Accordingly, a contact resistance between the gate electrode and the metal line increases, thereby increasing a resistance of the metal line. As a result, an operation speed of the semiconductor device is lowered. However, there is a growing demand on the high integration and the rapid operation speed of the semiconductor device.
To meet this demand, a refractory metal layer is formed in the contact hole or via-hole, to decrease the contact resistance. For example, a method of forming a plug of a tungsten layer is used in general.
A method of forming a plug according to the related art will be described as follows.
FIG. 1 is a cross sectional view of a defective contact having a void in a contact hole of a semiconductor device according to the related art.
As shown in FIG. 1, an insulating interlayer 11 is deposited on a semiconductor substrate 10 having a contact region. Then, a contact hole 12 for exposing the contact region is formed in the insulating interlayer 11. To decrease a contact resistance, a barrier metal layer 13 is deposited on an inner surface of the contact hole 12 and an upper surface of the insulating interlayer 11 by a reactive sputtering process, and a tungsten layer 15 is thickly deposited on the insulating interlayer 11 at a thickness suitable for filling the inside of the contact hole 12. At this time, the barrier metal layer 13 is formed of titanium nitride (TiN) or tungsten nitride (WN).
However, if the contact hole 12 has a size (diameter) below 0.2 μm, and has a great depth, an aspect ratio (ratio of a depth to a size of the contact hole) of the contact hole is above 5. In case of the contact hole having the high aspect ratio above 5, it is impossible to form the barrier metal layer 13 on the entire inner surface of the contact hole 12 with uniformity and continuity. That is, the barrier metal layer 13 is not deposited on some of the inner surface of the contact hole 12. As a result, the tungsten layer 15 is not formed in the entire space of the contact hole, whereby it is difficult to fill the contact hole 12 completely. That is, an empty space such as a void 16 appears in a lower side of the contact hole 12, whereby it may cause the electric disconnection of the metal line in the contact hole 12, or it may cause the degradation of reliability of the metal line to electromigration or stressmigration.